1. Field of the Invention
The present invention relates to a scroll-type fluid transferring machine which is used as an air compressor, a refrigerant compressor or an expansion machine.
2. Description of the Prior Art
The construction and function of a conventional scroll-type fluid transferring machine will be described with reference to FIGS. 9 to 14.
FIG. 9 shows the principle of a scroll-type fluid transferring machine. In the Figure, a reference numeral 1 designates a stationary scroll member, a numeral 2 designates an oscillatable scroll member, a numeral 5 designates a compression chamber formed between the wraps of the stationary and oscillatable scroll members 1, 2, a numeral 6 designates an intake chamber, and a numeral 8' designates a discharge chamber formed at the innermost part of the both scroll members. A symbol O indicates the center of the stationary scroll member 1. The stationary and oscillatable scroll members 1, 2 have the same spiral wrap of an involute of a circle or combination of the other suitable curved configuration. They are assembled with face-to-face and 180.degree. shifted condition to thereby form the compression chamber between the wraps of the scroll members. In the above-mentioned condition, the oscillatable scroll member 2 is subjected to an oscillating movement as shown in FIGS. 9a-9d in which the oscillatable scroll member moves around the center of the stationary scroll member 1 without movement of rotation, namely, a posture in angle of the scroll member 2 is fixed. With such oscillating movement, the volume of the compression chamber 5 is gradually reduced and a fluid introduced from the intake chamber 6 is discharged through the discharge chamber 8' at the center of the stationary scroll member 1.
FIG. 10 shows a conventional scroll-type compressor disclosed in Japanese Unexamined Patent Publication No. 103981/1984. The compressor is to compress gas such as freon and is used for refrigeration, air conditioning or an air compressor. In FIG. 10, a reference numeral 1 designates a stationary scroll member, a numeral 1a a base plate for the stationary scroll member 1, which constitutes a part of a shell as described below, a numeral 2 an oscillatable scroll member, a numeral 3 a base plate of the oscillatable scroll member 2, a numeral 4 a shaft of the oscillatable scroll member 2, a numeral 5 a compression chamber, a numeral 6 an intake chamber of the compression chamber 5, a numeral 7 an intake port, a numeral 8 an outlet port, a numeral 8' a discharge chamber, a numeral 9 a thrust bearing for supporting the back surface of the base plate 3 of the oscillatable scroll member 2, a numeral 10 a bearing supporter fixed to the stationary scroll member 1 by means of bolts and so on, a numeral 11 an Oldham's coupling which prevents movement of rotation and causes movement of oscillation of the oscillatable scroll member 2, a numeral 12 an Oldham's chamber formed between the base plate 3 of the oscillatable scroll member 2 and the bearing supporter 10, a numeral 13 an oil returning port formed in the bearing supporter 10 to communicate the Oldham's chamber 12 with a motor chamber 25 which is described below, a numeral 14 a crank shaft for driving the oscillatable scroll member 2, a numeral 15 an oil passage formed eccentrically in the crank shaft 14, a numeral 16 a bearing portion for oscillating movement which is formed eccentrically in the crank shaft 14 and receives the shaft 4 of the oscillatable scroll member, a numeral 17 a main bearing which fittingly receives the upper part of the crank shaft 14, a numeral 18 a bearing provided at the lower side of a motor which supports the lower part of the crank shaft 14, a numeral 19 a stator of the motor, a numeral 20 a rotor of the motor, a numeral 21 a first balancer firmly connected to the crank shaft 14 at the upper part of the rotor 20, a numeral 22 a second balancer firmly connected to the crank shaft 14 at the lower part of the rotor 20, a numeral 23 a shell which includes the stationary scroll member 1, the bearing supporter 10, the stator 19 of the motor and the bearing 18 at the side lower of the motor and which seals the entirety of the compressor, a numeral 24 designates oil stored in an oil reservoir in the bottom of the shell 23, and a numeral 25 designates the motor chamber containing the stator 19, the rotor 20 and so on.
The operation of the scroll-type compressor having the construction as above-mentioned will be described. When a current is supplied to coils of the stator 19, a torque is produced in the rotor 20, and the rotor 20 is rotated with the crank shaft 14. The rotation of the crank shaft 14 transmits the torque to the shaft 4 of the oscillatable scroll member 2 fittingly engaged with the bearing portion 16 of oscillating movement which is formed eccentrically in the crank shaft 14, whereby the oscillatable scroll member 2 is subjected to movement of oscillation by means of the Oldham's coupling 11 as a guide to perform a compressing function as shown in FIGS. 9a-d.
In the movement of the scroll members, gas sucked into the intake chamber 6 formed at the outer circumferential part of the oscillatable scroll member 2 through the intake port 7 is confined in the compression chamber 5. The gas is supplied to the inside of the scroll member as the crank shaft 14 rotates and is discharged through the outlet port 8 formed at the center of the stationary scroll member 1. The movement of oscillation of the oscillatable scroll member 2 is apt to cause vibration of the compressor itself by unbalance in rotation of the crank shaft 14. For the purpose of preventing the undesired vibration, the first and second balancers 21, 22 are attached to the crank shaft 14 to balance the rotation of it, thereby providing normal operation of the compressor without causing abnormal vibration.
FIGS. 11-12 show important parts of the compressor in detail. FIG. 11a is a longitudinal cross-sectional view of the oscillatable scroll shaft 4, the crank shaft 14 and a part of the wraps of the stationary and oscillatable scroll members in the condition that the oscillatable scroll shaft 4 is pushed to the bearing portion of oscillating movement 16 due only to the centrifugal force acting on the oscillatable scroll member 2 and the base plate 3 without compressing gas. FIG. 11b is a transversal cross-sectional view of the part shown in FIG. 11a.
In the drawings, a symbol O.sub.1 designates the center of the main bearing 17, a symbol O.sub.2 desigantes the center of the crank shaft 14, a symbol O.sub.3 designates the center of the bearing portion 16 of movement of oscillation, a symbol O.sub.4 designates the center of the oscillatable scroll shaft 4, symbols FC designates a centrifugal force acting on the oscillatable scroll member 2 and the base plate 3 and so on, a symbol r designates the quantity of eccentricity of the bearing portion 16 of the movement of oscillation to the crank shaft 14, a symbol d.sub.1 designates a gap formed between the bearing portion 16 and the outer circumference of the oscillatable scroll shaft 4, a symbol d.sub.2 designates a gap formed between the inner surface of the main bearing 17 and the outer circumference of the crank shaft 14, a symbol B designates a width of the groove between the wrap of the stationary scroll member 1, a symbol t designates the thickness of the wrap of the oscillatable scroll member 2, and symbols C and C.sub.1 designate gaps formed between the wraps of the stationary and oscillatable scroll members 1, 2, the gaps being generally in a relation of C=C.sub.1.
In the conventional scroll-type compressor, the actual width D of the oscillatable scroll member 2 is expressed as follows: ##EQU1##
Accordingly, the gap C in the radial direction between the wraps of the stationary and oscillatable scroll members 1, 2 can be given as follows; ##EQU2##
In the conventional scroll-type compressor, determination has been made in such a manner that in the equation (2), (B-2r-t) is greater than (d.sub.1 +d.sub.2). Therefore, the gap C in the radial direction is always formed between the wraps of the stationary and oscillatable scroll members 1, 2. Further, a load Fg for compressing gas acts on the oscillatable scroll shaft 4 in the direction perpendicular to the centrifugal force FC in addition to the centrifugal force in a state of normal operations as shown in FIG. 12, a resultant force F by composing the both forces Fg and FC is produced in the direction as shown in FIG. 12, whereby the oscillatable scroll shaft 4 is pushed to the direction of the resultant force F. Accordingly, the gap C' in the radial direction between the wraps of the stationary and oscillatable scroll members 1, 2 in the above-mentioned state becomes greater than the gap C in the radial direction in the state that only the centrifugal force FC exists. Thus, when the gap C or C' in the radial direction between the wraps is produced, there takes place no contacting state of the wraps of the stationary and oscillatable scroll members 1, 2 during the operation of the compressor. In this case, although a problem of wearing of the side surfaces of the wraps does not occur, it is difficult to perform sealing the gaps in the radial direction of the compressor chamber 5, and the gas in the chamber 5 leaks to the side of the intake port through the gap C or C'. When the gas in the compression chamber 5 leaks at the downstream side, the quantity of the gas to be discharged through the outlet port 8 is decreased whereby volumetric efficiency decreases. This results in recompression of a part of the gas leaked thereby causing increase in power input to the motor and decreasing a coefficient of performance.
In order to eliminate the above-mentioned difficulty, there has been proposed a method of sealing the radial gap in the radial direction wherein (d.sub.1 +d.sub.2) is determined greater than (B-2r-t) in the equation (2). However, in practice, there is scatter in values in accuracy of machining of the width of groove B, the quantity of eccentricity r and the thickness of the wraps d. Accordingly, the value (B-2r-t) indicates a value obtained by summing each scattered value. Accordingly, it is necessary to determine sufficiently large values for the gaps d.sub.1 and d.sub.2 in order to always make the value (d.sub.1 +d.sub.2) greater than the value (B-2r-t) at any position of rotation of the crank shaft. On the other hand, the optimum value is given to the gaps in the bearing d.sub.1 and d.sub.2 so that function of lubrication as the primary object can be satisfactorily performed. Accordingly, if the gaps in the bearing portion is made unnecessarily large, the function of lubrication may be impaired. It is, therefore, necessary to increase accuracy in machining of the width B, the quantity of eccentricity r and the thickness t. Further, if the position of the center O of the stationary scroll member 1 or the axial center O.sub.1 of the main bearing 17 is unexpectedly deflected, there happens that the gap C is not equal to the gap C.sub.1 (FIG. 11a), and in an extreme case, only either one is greater than the other, whereby the gaps C and C.sub.1 are not made 0 even though the optimum gaps d.sub.1, d.sub.2 are given.
Accordingly, it is necessary that accuracy in assembling the stationary scroll member 1 with respect to the axial center O.sub.1 of the main bearing 17 is increased.
Japanese Unexamined Patent Publication No. 162383/1984 proposes a way to eliminate the above-mentioned disadvantage. Namely, an eccentric bush having a bearing portion, the center of which is eccentric at a predetermined amount, is fitted in an eccentric recess formed in the crank shaft 14 and an oscillating scroll shaft is fitted in the bearing portion of oscillating movement, whereby the actual width for oscillation D for the oscillatable scroll member 2 can be varied as desired while the gap in the radial direction of the compression chamber 5 is rendered to be 0. The technique proposed in the publication will be briefly described with reference to FIGS. 13a, 13b, 14a and 14b. FIG. 13b shows a state that an eccentric bush 26 is rotatably fitted in an eccentric recess 16' formed in the crank shaft 14 and the oscillatable scroll shaft 4 is rotatably fitted into the bearing portion of oscillating movement 16" formed in the eccentric bush 26 with the quantity of eccentricity. FIG. 13a is a cross-sectional view of FIG. 13b. FIGS. 14a and 14 b show operations of the important part of the eccentric bush and the bearing portion. FIG. 14a shows a state that the wrap of the stationary scroll member 1 is slightly shifted toward the center of the scroll member due to scatter in machining or assembling, hence the oscillatable scroll member 2 is also shifted to the center, whereby the bush 26 is counterclockwisely rotated and the radius of oscillating movement R' is small. FIG. 14b shows a state that the wrap of the stationary scroll 1 is slightly shifted away from its center. In this case, the oscillatable scroll member 2 causes the eccentric bush 26 to rotated clockwisely due to a force F acting on itself and is in contact with the stationary scroll member 1 in the radial direction. Thus, with the eccentric bush, it is possible to always perform sealing in the radial direction of the compression chamber. However, in fact, since the force F imparted by the oscillatable scroll shaft 4 acts on the eccentric bush 26, a frictional force (not shown) is produced between the outer circumference of the eccentric bush 26 and the eccentric recess 16'. Accordingly, a resistance of friction is against the sliding movement of the outer circumference of the eccentric bush and it tends to block the rotation of the eccentric bush. If coefficient of friction between the outer circumference of the eccentric bush 26 and the eccentric recess 16' becomes excessive due to material of the bush to be used, accuracy in machining, condition of oil supply, etc., the eccentric bush is prevented from free rotation, and, as a result, there occurs operations under the condition that the wrap of the stationary scroll member is not in contact with the wrap of the oscillatable scroll member, hence sealing in the radial direction of the compression chamber 5 can not be established, whereby coefficient of performance is decreased as described before.
If the coefficient of friction is not so large and the compressor is operated under the condition that the wrap of the stationary scroll member is in contact with the wrap of the oscillatable scroll member, a load of contact F.sub.s will act on the contacting point between the wraps of the stationary and oscillable scroll members owing to a moment of rotation which is resulted by a force F' as shown in FIG. 14a. The load of contact F.sub.s constitutes a force of resistance against the sliding movement of the wrap of the oscillatable scroll member to the wrap of the stationary scroll member. The resisting force requires an additional input power in the operations of the compressor thereby reducing coefficiency of performance.
Japanese Examined Publication No. 28433/1983 has proposed a technique to solve the problem on the above-mentioned eccentric bush. The publication discloses a scroll-type compressor having a crank shaft provided with a fitting plate in an eccentric form and a oscillatable link engaged with a pivot pin attached to the fitting plate, wherein an oscillatable scroll member is fitted to a bushing provided at an end of the oscillatable link. In such scroll-type compressor, a resistance of friction produced at the time of oscillating movement of the oscillatable link becomes extremely small since the link is engaged with the pivot pin having a relatively small diameter. Accordingly, the oscillatable scroll member is movable in the radial direction so as to be in contact with the stationary scroll member to thereby establish sealing in the radial direction. However, in such scroll-type compressor, while the crank shaft bears a load from the oscillatable scroll member through the oscillatable link and the pivot pin, a bearing for supporting a main shaft is in a position shifted from the axial direction. Accordingly, the crank shaft will receive a large moment, whereby a large load is imparted to the bearing, resulting in occurrence of burning of the bearing.
Thus, the conventional scroll-type compressor has the drawback that it is difficult to perform sealing of the gap in the radial direction of the compression chamber thereby causing reduction in volumetric efficiency, hence reduction in coefficient of performance. Further, in the conventional scroll-type compressor using the eccentric bush to seal the compression chamber, it is difficult to obtain stable sealing due to a friction produced in the outer circumference of the eccentric bush to thereby also cause reduction in the volumetric efficiency.